One out of n checking apparatus and method

Abstract From the Canadian patent

A one out of N checking circuit for determining whether exactly one of N signal lines is active at any given time. The circuit includes a hierarchal structure of nodes which pairs the N signal lines together in a series of steps. Each node includes a pair of output signal lines. The first signal line carries a signal representing whether an active signal line was "seen." The second signal line carries a signal representing whether an error has occurred i.e. multiple active lines were seen. After each step the, number of signal lines is reduced by one-half until only two signal lines remain. At that point the two signal lines are compared and a final error signal is transmitted.